The present invention relates to the making of cladded, seamless steel tubes or pipes.
German printed patent applications Nos. 17 58 190 and 20 03 607 describe a variety of ways to prepare a blank to be worked into a clad tube. German printed patent application No. 17 77 114 proposes to place one tube inside another one and to bond them through expansion (of the inner one) or reduction (of the outer one). All of these methods refer primarily to cladding the inside of tubing.
Problems have arisen in all of these cases, particularly when applied for outside cladding of blanks to be processed further. The metallic bond between base metal and cladding material was found to be insufficient. An insufficient bond results, for instance, from differentials in the thermal coefficients of expansion. If the outer cladding, upon heating, expands more a gap may readily form between cladding layer and base. It can readily be seen that the exact same property, namely larger expansion of the cladding material, works favorably for inside cladding as the material is forced into more intimate contact with the base.